Exoproteome analysis of Clostridium cellulovorans in natural soft-biomass degradation

Clostridium cellulovorans is an anaerobic, cellulolytic bacterium, capable of effectively degrading various types of soft biomass. Its excellent capacity for degradation results from optimization of the composition of the protein complex (cellulosome) and production of non-cellulosomal proteins according to the type of substrates. In this study, we performed a quantitative proteome analysis to determine changes in the extracellular proteins produced by C. cellulovorans for degradation of several types of natural soft biomass. C. cellulovorans was cultured in media containing bagasse, corn germ, rice straw (natural soft biomass), or cellobiose (control). Using an isobaric tag method and a liquid chromatograph equipped with a long monolithic silica capillary column/mass spectrometer, we identified 372 proteins in the culture supernatant. Of these, we focused on 77 saccharification-related proteins of both cellulosomal and non-cellulosomal origins. Statistical analysis showed that 18 of the proteins were specifically produced during degradation of types of natural soft biomass. Interestingly, the protein Clocel_3197 was found and commonly involved in the degradation of every natural soft biomass studied. This protein may perform functions, in addition to its known metabolic functions, that contribute to effective degradation of natural soft biomass.